Duration Switchable High-Energy Passively Mode-Locked Raman Fiber Laser Based on Nonlinear Polarization Evolution

We experimentally demonstrate a stable passively mode-locked Raman fiber laser delivering high-energy pulses that can be switched between the regime of hundreds of nanoseconds and that of picoseconds by the nonlinear polarization rotation technique. Maximum average output power values of 304 and 53 mW are obtained, respectively, for the two typical mode-locking states with the pulse duration of 500 ns and 180 ps at the fundamental repetition rate of 275 kHz. The corresponding single pulse energy is as much as 1.1 μJ and 193 nJ, respectively. To the best of our knowledge, this is the highest pulse energy achieved from mode-locked Raman fiber lasers reported so far.